ABSTRACT / SUMMARY / PROJECT DESCRIPTION A single intramuscular injection of an adeno-associated virus (AAV) vector that expresses eCD4-Ig has the potential to treat or prevent HIV-1 infection for a lifetime. eCD4-Ig is a synthetic antibody or ?immunoadhesin? constructed by fusing parts of the viral receptor (CD4) and coreceptor (CCR5) to the constant region of an antibody. Because eCD4-Ig binds the HIV-1 envelope glycoprotein (Env) through the same contacts used by Env to recognize its receptor and coreceptor, eCD4-Ig neutralizes 100% of HIV-1 isolates and presents fundamental barriers to viral escape. We have previously shown that rhesus macaques inoculated with AAV expressing eCD4-Ig exhibited sterilizing protection against high-dose intravenous challenges with simian- human immunodeficiency virus (SHIV). Now, we propose several practical innovations designed to maximize the concentrations of eCD4-Ig in plasma that are sustained over the long term by AAV-transduced muscle.